North Korea is building two new submarines, including one capable of firing ballistic missiles.
A South Korean lawmaker made the announcement following a briefing by South’s National Intelligence Service.
North Korea has a large submarine fleet.
However, only one known experimental submarine capable of carrying a ballistic missile.
Since 2006, the country has been subject to UN Security Council sanctions over its nuclear and ballistic missile programmes.
North Korean leader Kim Jong Un and US President Donald Trump have met thrice since 2018.
They failed to make progress on US calls for Pyongyang to give up its nuclear weapons and North Korea’s demands for an end to sanctions.